1. Field of the Invention
The present invention relates to a paper feed mechanism for feeding continuous forms of paper, known as fan-fold paper, on a printer, a typewriter, or the like.
2. Prior Art
Paper feed mechanisms for continuously feeding fan-fold paper in the form of a series of joined papers of paper are generally classified into two categories. The paper feed mechanisms in one of the groups comprise a pin-feed tractor unit having a set of pins for engaging in perforated holes in the paper and pulling the paper across the print head of a printer, a typewriter, or the like. The paper feed mechanisms belonging to the other class comprise a pin-feed tractor unit which is designed to push the paper into the printing position in a printer, a typewriter, or the like.
FIGS. 6 and 7 of the accompanying drawings show one conventional paper feed mechanism, and FIG. 8 illustrates continuous forms of paper, i.e., fan-fold paper. The continuous forms of paper, indicated at 1 in FIG. 8, have a series of perforations 1a defined in each of their opposite side edges. In each of FIGS. 6 and 7, the fan-fold paper 1 is held against and travels around a cylindrical platen 2. The perforations 1a are engaged by successive pins 12a disposed on the outer peripheral surfaces of pin belts 12. The pin belts 12 are trained around a drive roller 13 which is coupled to a motor (not shown) and two idle rollers 14 which are rotatably supported on a frame (not shown). A print head 3 is positioned opposite to the platen 2 with the fan-fold paper 1 therebetween, for printing the fan-fold paper 1 as it is successively fed by the paper feed mechanism. The fan-fold paper 1 is held down against the pin belts 12 by angularly movable paper holders 15, 16 so that it will not disengage from the pins 12a during operation of the paper feed mechanism.
The paper feed mechanism shown in FIG. 6 is arranged to pull the fan-fold paper 1 to feed it over the platen 2 across the print head 3. To set the fan-fold paper 1 in position, it is threaded upwardly between the platen 2 and the print head 3, and, while the paper holders 15, 16 are being turned upwardly away from the pin belts 12, the perforated holes 1a in the fan-fold paper 1 are aligned with and fitted over the pins 12a on the pin belts 12. Then, the paper holders 15 are brought down over the pin belts 12, holding the fan-fold paper 1 against removal. When the pin belts 12 are rotated in the direction indicated by the arrows A by the drive roller 13, the fan-fold paper 1 is pulled by the pin belts 12 in the direction indicated by the arrows B. The fan-fold paper 1 is now fed along so as to travel between the platen 2 and the print head 3.
The paper feed mechanism shown in FIG. 7 is arranged to push the fan-fold paper 1 to feed it under the platen 2 across the print head 3. To set the fan-fold paper 1 in position, the paper holders 15, 16 are turned upwardly away from the pin belts 12, and the perforations 12a are aligned with and fitted over the pins 12a. The paper holders 15, 16 are then turned down over pin belts 12, holding the fan-fold paper 1 against removal. The fan-fold paper 1 is taken under the platen 2 and then guided upwardly between the platen 2 and the print head 3. When the pin belts 12 are rotated in the direction indicated by the arrows C by the drive roller 13, the fan-fold paper 1 is pushed by the pin belts 12 in the direction indicated by the arrows D. The fan-fold paper 1 is now fed along so as to travel between the platen 2 and the print head 3.
With the conventional structures shown in FIGS. 6 and 7, however, since the three rollers 13, 14 are used to drive and support the pin belts 12, the pin belts 12 are relatively long. Therefore, the pin belts 12 tend to elongate, sag, and vibrate. The vibration of the pint belts 12 causes the fan-fold paper 1 to move over back and forth. When the fan-fold paper 1 moves over during printing operation, any letters, numerals, or images are printed on the fan-fold paper 1 by the print head 3 with low quality.